1. Field of the Invention
The present invention relates to a semiconductor device fabrication, and more particularly, a semiconductor device fabrication system and a method of forming a semiconductor device pattern using the same for providing a desired size of a semiconductor device pattern through the irradiation of Ultra Violet (UV) light on a photoresist pattern, and then, performing a flow process, and a photoresist for manufacturing semiconductor devices thereby.
2. Description of the Related Art
Generally, a semiconductor device is manufactured by an array of processes such as deposition, photolithography, etching, and ion-implantation, etc.
That is, a pattern of the semiconductor device is formed by depositing a polycrystalline film, an oxide film, a nitride film, and a metal film, etc. on a semiconductor wafer, and carrying out a photolithography process, an etching process, and an ion-implantation process, etc. thereon. The photolithography process has a significance in the semiconductor device fabrication process, in which a predetermined pattern for semiconductor device integrated circuits is formed on the wafer using a Photo Mask.
The photolithography process is used in various semiconductor device fabrication processes for 16M DRAM, 64M DRAM, and further 256M DRAM and 1G DRAM or higher according to the light source used in an exposure processing step. Currently used light sources for the photolithography process are g-line(436 nm), i-line(365 nm), DUV(248 nm) and KrF laser(193 nm), etc.
Photoresist used in the photolithography process is made of highly polymerized photo-sensitive substance solubility of which is changed by the chemical reaction with light.
That is, light is projected on the photo mask having micro-circuits preformed, and the photoresist substance of the light-incident portion is changed into more fusible substance or more infusible substance compared with the photoresist substance of the light-nonincident portion. Then, it is developed with an appropriate developer thereby forming positive or negative type photoresist pattern. The photoresist pattern made as above functions as a mask in the following processes after the photolithography process, such as etching and ion-implantation processes, etc.
The types of the photoresist are divided according to the exposure light source such as g-line, i-line, and DUV. However, the above photoresist generally has a difficulty in forming a photoresist pattern having a size shorter than the wavelength of the exposure light source.
Currently, the resolution of a contact hole pattern in the photolithography process is lower than that of a line and space pattern so that the pattern uniformity over all of the wafer surface is not good.
Therefore, there is a demand for new technology to allow the formation of the contact hole pattern having a size of 0.20 xcexcm or less which is required for the highly-integrated semiconductor devices over 64M DRAM in order to overcome the limit resolution of the photoresist.
Currently, the method for forming the contact hole having a smaller size than the wavelength of the exposure light source is as follows.
First, as flow process method for a photoresist pattern, a normal photoresist pattern of contact holes having a size bigger than wanted is formed using a normal chromium (Cr) mask, and then, heat over the softening point of the photoresist is applied on the photoresist pattern so as to occur the softening of the highly polymerized photoresist and reduce its viscosity and flow it. As a result, the size of the photoresist pattern is reduced.
Second, as a modified exposure method, exposed portion and non-exposed portion are clearly defined by exposing using a modified illumination and a Phase Shift Mask (PSM). As a result, a photoresist pattern has a smaller size of contact hole than using a normal light and a photo mask.
The flow method by i-line photoresist including novolak resin, photo active compound (PAC), solvent and additives uses the speed difference due to the increase of thermal properties attributable to the pyrolysis of the PAC by heat and the Cross-Linking reaction of the resin and the PAC, and the photoresist pattern flow phenomenon by the decrease of the viscosity by heat.
The flow of the i-line photoresist proceeds with the Cross-Linking reaction, and the flow phenomenon is properly controlled by the Cross-Linking reaction. That is, because the flow phenomenon of the i-line photoresist gradually proceeds with the temperature changes, it is little affected by the temperature changes of the process and the facilities.
In case of the i-line photoresist, 0.25 xcexcm of pattern can be obtained by the flow method. By applying a modified light and the PSM on the i-line photoresist, 0.28 xcexcm of pattern can be achieved.
FIG. 1 shows the conventional pattern formation method for semiconductor devices, and in other words, shows a processing sequence of the contact hole formation method using the i-line photoresist.
Referring to FIG. 1, first, as step of coating a wafer with photoresist (S2), with the i-line photoresist is coated on the wafer having Hexamethyldisilazane (HMDS) pre-deposited thereon. Then, as step of soft-baking the photoresist (S4) on the wafer, the solvent included in the photoresist is removed by the soft bake so that the adhesiveness of the photoresist is improved, and the coating state of the photoresist on the wafer with a certain thickness is maintained. After the soft bake, as step of exposing after aligning a photo mask on the photoresist (S6), a wafer having the i-line photoresist thereon is moved to an i-line stepper, and the PSM having a fine pattern formed thereon is aligned over the wafer.
Then, the wafer having the photoresist thereon and the PSM aligned with the wafer is irradiated with an i-line light source so as to carry out the exposure. Then, as step of Post Exposure Bake (PEB) for the exposed wafer (S8), the wafer passing through the exposure is baked at a proper temperature so as to remove the wave pattern produced by standing wave phenomenon which occurs on the photoresist pattern during the reinforcement interference and the destruction interference by the incident light and the reflection light of the exposure light source, and improve the photoresist pattern profile, and further, improve the resolution of the photoresist pattern. Next, as step of the formation of the photoresist pattern by developing and cleaning the wafer passing through the PEB (S10), the wafer with the PEB completed is moved to a developing unit, a developer is supplied on the photoresist on the wafer so as to form a photoresist pattern, and the development by-products are removed using a cleaning solution.
Then, as step of hard bake for the developed wafer (S12), the photoresist pattern with the development completed is dried, and hardened so as to harden the photoresist pattern.
Then, as step of flow bake after the hard bake (S14), heat is applied on the photoresist pattern at a temperature over the softening point of the photoresist so as to reduce the softening and the viscosity of the highly-polymerized photoresist, and make the photoresist pattern flow thereby reducing the pattern size. However, in case of carrying out the flow method using the i-line photoresist and the PSM by a modified light, the photoresist pattern having 0.18 xcexcm of resolution can be formed, but the thermal properties of the pattern of highly-polymerized photoresist becomes nonuniform because part of the non-exposure portion is exposed nonuniformly. That is, during the exposure for the photoresist pattern formation, the exposed amount on the Cell portion of high-density pattern and the Peri portion of low-density pattern, non-exposure portion respectively is nonuniform. As a result, the nonuniformity of the exposed amount results in a flow rate difference in the hardness by heat, and so, a Bulk effect of the distortion of the contact hole pattern occurs in the interface of the Cell portion and the Peripheral portion.
In the meantime, when using a DUV photoresist, the DUV photoresist is more sensitive to heat than the i-line photoresist, and also sensitive to the temperature uniformity of a bake oven used in the flow process. As a result, the flow occurs abruptly, and it is difficult to get uniform contact hole pattern overall on the wafer surface. That is, the flow process when using the DUV photoresist, and the i-line photoresist respectively is different. Therefore, the DUV photoresist is difficult to expect as same effect as the i-line photoresist because of the lack of the mechanism in which the Cross Linking reaction happens at a temperature of the flow start or at a lower temperature.
FIGS. 2 to 5 are cross-sectional views showing the processes for the contact hole pattern formation by flow method using the i-line photoresist and the PSM according to the process sequence of FIG. 1.
As shown in FIG. 2, i-line photoresist 6 is deposited over a wafer 2 having a certain sublayer-4 formed thereon, and then, the photoresist is soft-baked. Then, as shown in FIG. 3, the wafer 2 is moved to an i-line stepper, and the PSM 7 having the fine pattern formed thereon is aligned over the wafer 2 having the i-line photoresist 6 thereon. Then, the exposure is carried out for the wafer using the i-line light source.
Then, as shown in FIG. 4, the PEB is carried out on the exposed wafer 2, and developing and cleaning are carried out successively so as to form a first contact hole pattern 8. At this time, the size of the first contact hole pattern 8 is 0.25 xcexcm. Then, as shown in FIG. 5, the first contact hole pattern 8 is flown and baked so as to form a second contact hole 9. However, in case of carrying out the flow using the PSM by the modified illumination, some of the non-exposure portion is nonuniformly exposed, and the thermal properties of the highly polymerized photoresist pattern becomes nonuniform. As a result, the flow rate difference occurs depending on the hardness by heat thereby causing a bulk effect, wherein the second contact hole 9 is distorted during the flow and bake, as shown in FIG. 5.
The present invention is directed to provide a semiconductor device fabrication system and a method of forming a semiconductor device pattern using the same, which substantially obviates one or more problems due to the limitations and the disadvantages of the related art.
One object of the present invention is to provide a method of forming a semiconductor device pattern through the formation of a uniform and a desired size of a contact hole pattern by allowing a flow method in case of using both of an i-line photoresist and a Phase Shift Mask (PSM).
Another object of the present invention is to provide a method of forming a semiconductor device pattern through the formation of a uniform and a desired size of a contact hole pattern by applying a flow method for a Deep Ultraviolet (DUV) photoresist.
Still another object of the present invention is to provide a semiconductor device fabrication system for the method of forming a semiconductor device pattern of the present invention.
Still another object of the present invention is to provide a photoresist being used in forming a semiconductor device pattern for manufacturing semiconductor devices.
To achieve these and other advantages and in accordance with the purpose of the present invention as embodied and broadly described, a semiconductor device fabrication system includes: a photoresist coating unit for coating a wafer with a specific photoresist; a developing unit for forming a photoresist pattern on the wafer coated with the photoresist; and a cross-linking unit for cross-linking the photoresist pattern to provide a stabilized flow during the flow process for the photoresist pattern.
The semiconductor device fabrication system may be one of a spinner and a track system.
The fabrication system for manufacturing semiconductor devices preferably further includes: a HMDS coating unit for increasing the adhesiveness of photoresist on the surface of a wafer transferred from a wafer loading unit before delivery of the wafer to the photoresist coating unit; a bake unit for baking the wafer having photoresist thereon, and passing the wafer through an exposure and a development; and a Wafer Edge Exposure (WEE) unit for exposing an edge portion of the wafer by a certain width.
The semiconductor device fabrication system preferably comprises at least one of the wafer loading unit, the HMDS coating unit, the photoresist coating unit, the coating unit, the bake unit, the Wafer Edge Exposure unit, and the cross-linking unit respectively.
Preferably, the soft bake unit of the semiconductor device fabrication system includes: a soft bake unit for removing solvent included in the photoresist on the wafer; a Post Exposure Bake (PEB) unit for removing fine standing waves present on the photoresist pattern; and a hard bake unit for hardening the photoresist pattern.
The cross-linking unit may be a UV bake unit for irradiating the developed wafer with UV light.
The UV bake unit includes: a UV lamp placed on the upper part of the UV bake unit, and producing UV light; and a hot plate placed on the lower part of the UV bake unit, and heating the wafer which is mounted at a distance away from the UV lamp. The UV lamp may be a Microwave-Excited Lamp or Mercury-Xenon Lamp.
In another aspect of the present invention, a semiconductor device fabrication system includes: a cross-linking unit for cross-linking a photoresist pattern on a wafer having passed through development to provide a stabilized flow during the flow process for the photoresist pattern; and a process chamber for carrying out an etching process for a sublayer on the wafer using the photoresist pattern as an etch mask, the position of the process chamber in the system facilitating transfer of the wafer between the cross-linking unit and the process chamber.
The fabrication system for manufacturing semiconductor devices of the present invention further comprises a load lock chamber connecting the cross- linking unit and the process chamber.
The cross-linking unit may be a UV bake unit for irradiating the developed wafer with UV light.
The UV bake unit includes: a UV lamp placed on the upper part of the UV bake unit, and producing a UV light; and a hot plate placed on the lower part of the UV bake unit, and heating the wafer which is mounted with a distance from the UV lamp.
In another aspect of the present invention, a method of forming a semiconductor device pattern includes: a) coating a wafer with a photoresist; b) aligning a photo mask on the photoresist, and carrying out an exposure; c) forming a photoresist pattern on the wafer; d) carrying out a cross-linking of the photoresist pattern; and e) carrying out a flow bake for the photoresist pattern after the cross-linking.
The photoresist is preferably for i-line or Deep Ultraviolet (DUV), and the photo mask uses a Phase Shift Mask (PSM) in case of using the i-line photoresist.
The i-line photoresist is preferably a positive photoresist including a base resin, a photo active compound(PAC), and a solvent, and, as an additive for activating the Cross Linking reaction of the photoresist pattern, 2,4,6-triamino-1,3,5-triazine is added.
The photoresist pattern may be a contact hole pattern, and the cross-linking may be a UV-bake of the photoresist pattern.
Preferably, the UV bake includes irradiating the photoresist pattern with UV light and performing a bake process of heating the photoresist pattern simultaneously.
The method may include hard-baking prior to the UV bake. Preferably, the heating provides heat between 50 to 140xc2x0 C., and the step of irradiating UV light is carried out for 10 to 80 sec. A process temperature of the flow bake may range from 140 to 200xc2x0 C., and a process time for the flow bake ranges from 80 to 120 sec. The flow bake is preferably carried out at least one time repeatedly.
The cross-linking may include: a) hard-baking the photoresist pattern; and b) carrying out a development for the photoresist pattern passing through the hard-bake.
The development for the photoresist pattern passing through the hard-bake may be carried out at least two times repeatedly.
In another aspect of the present invention, i-line photoresist is a positive photoresist, including a base resin, a photo active compound(PAC), and a solvent. As an additive for activating the Cross Linking reaction of the photoresist pattern, 2,4,6-triamino-1,3,5-triazine can be added.
Here, the amount of the 2,4,6-triamino-1,3,5-triazine is preferably between 0.001 to 5 weight percent for the whole amount of the base resin, the photo active compound(PAC), and the solvent.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.